But hmm…just one caveat to those hungry for laughs. It’s been suggested that, like “I Love You, Man” (2009), only more so, to fully enjoy this tale of a bachelor party weekend in Las Vegas it might help to be a guy…or at least know one really well. The fantasy depicted is as much about male bonding as it is about Bacchanalian behavior.

You see, though Phil (Bradley Cooper), Alan (Zach Galifianakis), Stu (Ed Helms) and Doug (Justin Bartha) may sense it on a subconscious level, their otherwise spontaneous adventure in naughtiness is a boisterously tacit declaration…their last rite of passage as young men. Phil is already married. Now Doug is taking the leap. Gee, this counts.

Not that they talk about it much. At least not in heart-to-heart fashion. It’s done in deed, on the run in exclamation, chide and bravado, Three Musketeers style, their very own d’Artagnan in tow. Years hence, it will be their watershed. For they are basically good boys. Which is why it’s a riot. Bad boys behaving badly are just a bore.

Surely, if they were not upstanding guys, Sid (Jeffrey Tambor), the bride’s dad, wouldn’t loan them his most prized possession. We don’t want anything to happen to the beautiful, 1969 Mercedes-Benz 280SE Cabriolet. Yet as the co-starring icon cruises off to that sinful oasis, we have been cued to trepidation.

Perhaps reliving a moment of youth, Sid winkingly reminds that, “What happens in Vegas stays in Vegas.” He makes but one stipulation. Pity, he’s referring to his own son when he instructs, “Just don’t let Alan drive. He’s not right.” Sid has something there. Nonetheless, Alan is along for the ride, the foisted pal, the wildcard.

The ensuing hijinks, delivered in cataclysmic waves of raucousness, begin with a flashback. Disheveled in the desert, his five o’clock shadow signaling what hath befallen, Phil is talking to Doug’s intended (Sasha Barrese). She needs assurance they’ll be back in time. He fears it’s not going to happen. Roll tape. We’re about to find out why.

Via a deft screenplay sporting the kind of chronological savvy rarely seen in comedies, it is a mystery how they first wind up in a hotel suite with a live tiger, a baby and the worst hangovers of their lives. It is also curiously ironic that Stu, a dentist, is missing a tooth and Phil is wearing a hospital bracelet. This is a case for Mr. Sherlock Holmes.

He’ll need a sense of humor and an open mind as the layers of complication peel off to our sidesplitting astonishment. We know no more than the boys. One moment they are on the hotel roof toasting the occasion. Next stop, complete amnesia and bewilderment. And uh, oh—Stu can’t find the engagement ring he was going to give his shrewish girlfriend.

That’s the dentist’s specific subtext. Each fellow brings a little baggage to the journey…something to work out between crazy and sometimes even death-defying escapades. Which include, but are not limited to, an unsavory gangster known as Mr. Chow (Ken Jeong), a big to-do with Mike Tyson and a stolen police cruiser.

Oh, and there seems to be some sort of connection with pretty Jade, who explains that being an escort is really just a good way to meet customers for her, er, other occupation. Heather Graham is winsome in a variation on the traditional, heart-of-gold stereotype. She’s also invaluable in helping the protagonists piece things together.

So is the quirky, foulmouthed Mr. Chow, though we’re not sure we can take his complete word on matters. For one, he says the gang owes him $80G’s—his share of last night’s gambling winnings. In the meantime, adding a bit of icing to the confusion, no one really knows what’s become of bridegroom-to-be Doug.

Note that for some the R-rated thrills might prove the guilty kind. Though never seen, there is alleged drug taking, plus a host of laws broken. However, for filmgoers who can separate entertainment from their real life values, this extreme delve into boys being boys will prove hilarious while also waxing philosophical about the gender.

Not that this could ever be mistaken for a doctoral thesis on the male animal. Or at least let’s hope not. Indeed, the buddy-buddy genre has evolved since Cary Grant, Victor McLaglen and Douglas Fairbanks, Jr. exchanged courtesies in “Gunga Din” (1939). “The Hangover” is an exceptionally zany aftereffect of that democratization.